Project Area51 is a collection of Open Source & Open Data projects ranging from software development, map generation & retro computing to processing real time data sets like tracking trains on the UK Rail network or processing telemetry from the International Space Station.
Why Project Area51
In the beginning each project had it's own domain, however whenever a new project was started it ended up sitting in a subdomain of another unrelated project. That domain usually ended up being called area51 simply to indicate that it was a secret project of some kind. After a while this became untenable with multiple instances spread over multiple domains so the original area51.onl domain was setup & the project got it's new name.